The present invention relates to hydraulic mounts for damping vibrations.
A variety of mount assemblies are presently available to isolate vibrations. One conventional mount commonly employed to reduce vehicular vibrations is the hydraulic mount.
Conventional hydraulic mounts provide relatively low-damping, vibration-isolating characteristics (low dynamic rigidity), at vibrations of low amplitudes and high frequencies such as those generated by a running engine. These mounts also provide substantially increased-damping characteristics (high dynamic rigidity) at vibrations of high amplitudes and low frequencies such as those generated by running a vehicle on bumpy inconsistent road surfaces.
A hydraulic mount assembly of prior invention includes a reinforced, hollow rubber body that is closed by a resilient chamber diaphragm so as to form a cavity. This cavity is partitioned by a pair of mating plates into two chambers that are in fluid communication with each other through a relatively large primary orifice in the partition. A primary chamber is formed between the partition and the hollow rubber body. A secondary chamber is formed between the partition and the chamber diaphragm.
A decoupler is positioned in the partition's primary orifice and reciprocates in response to vibrations so as to produce small volume changes in the two chambers. When the decoupler is moved toward the chamber diaphragm, it exactly compensates for the volume lost due to the compression of the primary chamber. The compensated volume is transferred to the secondary chamber by the displacement of the decoupler and then is accommodated by expansion of the chamber diaphragm. In this way, at certain low vibratory amplitudes the major fluid flow displaces the decoupler so that the mount exhibits low dynamic rigidity to isolate engine vibrations and hydraulic damping is not provided.
In addition to the primary orifice, a smaller inertia track provides an orifice which extends around the perimeter of the partition so as to have a large length-to-diameter ratio. Each end of the inertia track has an opening; one opening communicates with the primary chamber and the other with the secondary chamber. The inertia track provides the hydraulic mount assembly with a means of providing hydraulic damping for high dynamic rigidity at high amplitude vibrations where the volume lost due to the compression of the primary chamber exceeds the capacity of the decoupler's compensation. When combined, the oscillating decoupler and the inertia track provide at least two distinct dynamic modes of operation. The operating mode is primarily determined by the flow or lack of flow of fluid between the two chambers through the inertia track.
More specifically, small amplitude vibrating inputs, such as from the engine or the like, are isolated by the mount which exhibits low dynamic rigidity due to decoupling wherein, the decoupler reciprocates, compensating for volume losses, thereby preventing fluid motion in the inertia track, as described above. On the other hand, large amplitude vibrating inputs force the decoupler against either mating plate stopping volume compensation to produce fluid flow through the inertia track resulting in a high level of vibration damping force and high dynamic rigidity. In each instance, as the decoupler moves from one seated position to another, a relatively limited amount of fluid can bypass the inertia track by moving around the sides of the decoupler.
Conventionally decoupled hydraulic mounts have certain drawbacks. When the free decoupler closes against one of the partition's plates, noise referred to as "chortle" or "loose lumber" is created. Additionally, leakage between the partition's plates from the inertia track effects the low amplitude damping performance of the mount. This leakage is also a major source of part-to-part damping variation.